1. Field of the Invention
This invention relates to dial indicating instruments of the type used to measure temperature or other variables and more particular to bi-metallic thermometers.
2. Description of the Prior Art
A bi-metallic thermometer comprises an enclosure consisting of a stem terminating in a case. A bi-metallic helical temperature sensing coil disposed within the stem imparts rotary motion to a shaft. The shaft extends into the case and a pointer is secured to the end of the shaft. The sensing coil, the shaft and the pointer rotate with variations in temperature. The temperature is indicated on a graduated dial mounted opposite the pointer.
Since dial thermometers are likely to be mounted in many different positions to suit convenience of the particular job in which they are installed, it has generally been necessary for the manufacturer to manufacture a number of different types of dial gages and thermometers to meet industrial requirements. For instance, if a thermometer had to be placed over head, the dial gage had to be built so that the dial tilted downwardly so that it could be read; if the thermometer was to be mounted below the normal line of vision, the dial gage had to be built so that the dial tilted upwardly, etc.
The prior art has made efforts in the past to provide bi-metallic thermometers with multi-angular gages but such efforts have not generally proved satisfactory. In some cases, the thermometers have been inaccurate, the inaccuracy occurring in the calibration between the head and the stem when the head is tilted or rotated with reference to the stem. In other cases, the thermometers have been restricted to angular adjustment in only one place. Also, some thermometers have been subjected to an excessive amount of friction in the indicating mechanism when an adjustment is made between the head and the stem while other thermometers have been unsuited for repeated adjustment, accidental loads or easy cleaning.